Objects imaged using electromagnetic radiation, including visible light, infrared light, x-rays, gamma rays and radio frequency waves, can exhibit significant heterogeneity. For example, in the case of objects imaged with light, this heterogeneity manifests itself as microscopic—as well as macroscopic-level changes in optical properties, for example, variation in the coefficient of optical absorption or the coefficient of scattering throughout the object. Macroscopic-level changes in the coefficient of optical absorption have significant impact on the propagation of light through and around such areas. In particular, light tends to tunnel, or waveguide, through areas exhibiting lower optical absorption, thus taking the path of least resistance. Similar waveguiding effects can be observed with other forms of electromagnetic radiation propagating through heterogeneous media.
When acquiring a image of a diffuse heterogeneous object, such as animals, humans, and/or any biological tissue for example, using electromagnetic radiation, the object regions that the radiation has propagated to because of any waveguiding effects will appear disproportionately intense to the detector or detectors measuring the electromagnetic radiation. These regions of high apparent intensity, sometimes called “hot spots,” can give rise to regions of false or exaggerated intensity in the two dimensional images or in three dimensional tomographic image reconstruction of the object. This can cause misleading or false attribution of the electromagnetic radiation signal, and/or agent or probe distribution to such object regions, when such object regions might have very little or no agent or probe (including endogenous agents and exogenous agents). This waveguiding phenomenon holds for any electromagnetic radiation propagating through a heterogeneous object, regardless of whether or not there are exogenous or endogenous agents. The proportion or amount of agent/probe as well as its location would be inaccurate due to the waveguiding effects of electromagnetic radiation, causing artifacts in two dimensional images and tomographic images. Regions of objects more absorbent to electromagnetic radiation might cause waveguiding or tunneling into regions of less absorption, creating inaccurate or erroneous attribution of radiative signal. For example, in biological tissue such as the heart region of a mammal, cardiac muscle is more absorbant than skin or subcutaneous fat. Radiation, such as (but not limited to) light, traveling through the tissue would tend to tunnel, or waveguide, into regions of lower relative absorbance, such as the skin. This would give rise to inaccurate and false attribution of radiation concentrated in regions vulnerable to waveguided radiation such as skin folds or other thin tissue.
Thus, there is a need for systems and methods for compensating for the effects of waveguiding. This need is especially urgent for in vivo optical imaging of heterogeneous diffuse objects such as animals, humans and biological tissue.